The present invention relates to a radioactive source director module for use in a gas monitor and more particularly to such a detector module which is adapted to contain the radioactive source and other detector components, to permit sealed coupling of those components with other portions of a gas monitor and to prevent accidental or undesired exposure of the radioactive source.
Generally, the present invention relates to a tracer gas monitor designed to sample and determine the presence of an electron capture tracer gas. A sample or test gas, containing the tracer gas, is conventionally injected into a flow of carrier gas. The carrier gas containing the tracer gas is caused to flow through an electron capture detector containing spaced apart electrodes and a source of ionizing electrons such as a radioactive material.
The tracer gas is selected from a class of gases capable of absorbing electrons which would otherwise be collected upon one of the two electrodes. Thus, the presence of the tracer gas within the carrier gas flowing through the detector tends to reduce electron flow to one of the electrodes which is measured by conventional external electronic means. With electronic circuitry for the gas monitor being calibrated with respect to the carrier gas, the concentration of the tracer gas passing through the detector may be closely determined by suitable reference to a calibration chart.
Within such gas monitors, the carrier gas is conventionally an inert gas such as nitrogen or argon. The tracer gas may be a suitable gas capable of electron capture such as sulphur hexafluoride which is a non-radioactive, non-toxic inert gas. Other examples of suitable tracer gases include fluorocarbons such as those available under the tradename Freon as well as other halogenated compounds.
Gas monitors of the type described above are generally well known in the prior art as may be seen for example with reference to U.S. Pat. No. 3,714,421 issued Jan. 30, 1973.
The present invention is particularly concerned with the use of radioactive materials employed as electron sources in such monitors. Commonly, it is desirable for the gas monitors to be used by personnel who are otherwise untrained in the handling of radioactive materials. In addition, it is sometimes necessary to change the radioactive source within a gas monitor depending upon the particular application for which the monitor is being used.
Accordingly, there has been found a need for an improvement in such gas monitors permitting their use by such personnel while assuring against accidental or undesired removal of the radioactive material from the monitor or undesired or accidental exposure of the radioactive material.